Review Question - QID 215108

A 62-year-old man presents to the emergency department with a 1-day history of severe dyspnea. He says that he began to feel short of breath after eating Thanksgiving dinner and that he can only sleep while sitting straight up. He came to be evaluated today because he felt lightheaded while standing up and had palpitations of his heart. On presentation, his temperature is 97°F (36.1°C), blood pressure is 74/61 mmHg, pulse is 115/min, and respirations are 21/min. A physical exam reveals cool extremities with delayed capillary refill. He begins to feel extremely lightheaded and is started emergently on a medication. His blood pressure stabilizes but he develops headaches, tremors, bronchospasms, and hypokalemia. What is the mechanism of action for the most likely medication that was administered in this case?